Gabbro is an intrusive igneous rock that makes up large parts of the Earth's Crust, especially in deep oceanic areas. It is derived from molten magma that has cooled and crystallized before reaching the Earth's surface, and occurs in massive forms. Gabbro has a similar composition to that of basalt, being primarily made up of plagioclase feldspar, olivine, and pyroxene. There are usually also small amounts of other minerals present, such as magnetiteand ilmenite. It has a coarse grain structure, with the crystals being more than 1 mm in diameter. It is typically dark green to black, and can often contain valuable minerals, such as gold, silver, chromium, copper, cobalt, and nickel.